1. Field of the Disclosure
The invention relates to an optical arrangement according to the preamble of claim 1.
2. Description of Related Art
Optical arrangements and devices for varying an imaging ratio or of a refractive power have been known for a long time. The varifocal lenses, for instance, have already been mentioned since the first half of the 19th century in the Proceedings of the Royal Academy. Contrary thereto, an application for a patent for a first optical arrangement for continuously varying an imaging ratio with a stationary image was filed in 1902 (U.S. Pat. No. 696,788). An arrangement for varying an imaging ratio in discrete steps in the form of a drum comprising different pairs of optical elements by means of a refractive power also dates back at least to the first half of the 20th century (e.g.: DE 1 284 117, in which the issue of further intermediate steps in response to the varying of an imaging ratio is broached).
Attempts to change refractive power also took place many years ago (GB 1 318 042 and DE 2 320 626) without having found their way into the commercial field.
During the last decades, much progress has been made in the correction of the optical errors in optical arrangements for continuously varying an imaging ratio, so that the optical quality is acceptable, at least within a small tuning range of such an imaging ratio. The cost-effectiveness of the arrangements was also improved by partly using the same components, see U.S. Pat. No. 6,853,494 B2. The handling of the varifocal lenses became easier by means of autofocus. Only the optical arrangements for varying an imaging ratio or a refractive power in discrete steps have hardly changed. For instance, it becomes clear from EP 1 969 995 A1 or from the brochure “Augenuntersuchungen mit der Spaltlampe” of the ophthalmologic instruments by Carl Zeiss, design number: 000000-1152-354 that nothing has happened here for more than the last 50 years, except for the correction of optical errors.
These arrangements furthermore remained substantially unhandy and dissatisfying as a whole. Even though an optical arrangement for varying an imaging ratio and/or a refractory power in discrete steps according to the state of the art (FIG. 1) can encompass a wide dynamic range in the imaging ratio (large ratio maximum to minimum imaging ratio), wherein optimal optical quality can remain virtually constant across the entire dynamic range. The development effort of such an arrangement is thereby rather low. However, there are many large disadvantages. Only few discrete imaging ratios are possible, no intermediate values. Due to the fact that the axis of rotation of the arrangement intersects the optical path, extensive mechanical solutions are necessary. This is one of the reasons why the arrangement is unreasonably large, voluminous, long, heavy and slow. Due to large levers, it has large moments in response to being moved (rotation of the arrangement) and has thus a high inertia and problems arise in response to the stabilizing in the end position. It uses a lot of energy when it is moved. The imaging ratio rarely meets exactly the demand of the user. Due to the high inertia and the large moments of the arrangement, the device, which includes the arrangement, must be embodied in a particularly robust and stable manner. The arrangement itself is thus not only very large, it additionally makes the device, which accommodates it, larger and heavier. Such an arrangement can mostly be used in the low-end microscopes and in other stationary optical viewing devices. Due to the size, the weight, the energy consumption and the slowness, a use in the consumer field, thus cellular phones with a camera, cameras, camcorders, etc., e.g., is thus impossible.
On the other hand, a common optical arrangement for continuously varying an imaging ratio provides for a continuous detuning by means of a translatory movement of one or a plurality of components and a rotary movement of the arrangement is not necessary. The disadvantages, however, are serious: optical characteristics, e.g. optical errors, change with the imaging ratio, a high development effort is necessary, many, partly moved lenses are required. It is difficult to adjust the arrangement, the control thereof is complicated. The movements of the lenses must be encoded, because they must occur in a highly non-linear manner. High demands are made on the moved mechanics. The arrangement is slow, in particular in response to large variations in the imaging ratio. It is heavy, has a high wear and hysteresis occurs in parts. Optical errors in response to a wider dynamic are not acceptable, high chromatic aberrations and distortions (image field curvature) occur. A further disadvantage is the weakness in terms of light, which is shaped by a higher minimum number of f-stops and by many additional surfaces. The energy consumption in response to a full utilization of the dynamics is also very high. When used in cameras, the parts, which are moved against the housing, make it possible for dust, other small particles and liquids to penetrate into the housing. Furthermore, the arrangement is expensive, which is caused by the high development costs as well as by the component and production costs. This arrangement has been used for decades in the consumer as well as in the professional field, but only more or less hesitantly. For the most part, the offer is only a bad compromise of price, quality and handling.
The recent attempts of setting up an optical arrangement for continuously varying an imaging ratio comprising a small dynamic range and without moved parts (Sensors, Cameras, and Systems for Scientific/Industrial Applications VIII. Edited by Blouke, Morley M., Proceedings of the SPIE, Volume 6501, pp. 650109 (2007)), by means of lenses having a variable refractive power, can be considered as having failed, on the one hand, but as being a starting point for other solutions, on the other hand. The attempt has failed, because an intrinsically continuous arrangement is operated only in a switching operation with only two positions (1.times. and 2.5.times.) due to the very high chromatic aberrations, and in addition comprising four lenses having a variable refractive power, where only two are actually needed on principle. The number of the different imaging ratios are not the way they are desired. The authors even propose to record the different colors subsequently, so as to manage the chromatic errors. This is not a good proposal for a microscope, a headset magnifying glass or another viewing device, with which images are not recorded by means of a camera chip, but are observed directly with the eye. Having a length of 29 mm, the arrangement is also not suitable for a cellular phone camera, e.g.